Tailpipe fuel consumption effect

[lancer5790]

does the tailpipe affect the fuel consumption? I had the tail pipe (about 8inches long protrutding pipe after the muffler) of my 97 honda city cut off then replaced with an aftermarket stainless pipe with larger diameter. since then i noticed the fuel consumption went up. could this be due to the replacemenmt of tailpipe?

[ghosthunter]

The car exhaust system is not a simple thing.

You have to balance the exhaust velocity with the size of the piping and the engine's performance & typical use.

Too small diameter of pipe will cause restriction.

Too big diameter of pipe will cause the exhaust gasses to slow down too soon and cause more backpressure than you want.

An exhaust system that has too many bends will also cause the exhaust gasses to slow down.

An exhaust system with pipes that change diameters is not that good for performance but it might help adjust the exhaust note.

To simplify the exhaust system, a single diameter should be chosen that will match your engine's performance. For a 1.6L engine, a maximum of 2inch pipe diameter is optimum for performance. For better fuel economy, the stock diameter is best (I think it was 1.5 to 1.7 inches).

[ghosthunter]

does the tailpipe affect the fuel consumption? I had the tail pipe (about 8inches long protrutding pipe after the muffler) of my 97 honda city cut off then replaced with an aftermarket stainless pipe with larger diameter. since then i noticed the fuel consumption went up. could this be due to the replacemenmt of tailpipe?

Was the tailpipe tapered (narrow to wide)?

[lancer5790]

Was the tailpipe tapered (narrow to wide)?

yes, the entire protruding pipe was replaced with about 3"dia from the original 1.7" i think. but the point is, the cut pipe was already after the muffler?

[ghosthunter]

yes, the entire protruding pipe was replaced with about 3"dia from the original 1.7" i think. but the point is, the cut pipe was already after the muffler?

In all of my past exhaust mods, the tail-pipe was always the same size as the rest of the exhaust piping.

Is the new 3" pipe the same diameter in it's entire length? Or is it like a cone inside?

[duskylim]

Dear Sirs:

In my experience most 1995 and up model cars have very good exhaust systems, with excellent balance between power and fuel economy.

One of the worst modifications that can be done is to fit an aftermarket tailpipe purely for visual and sound effect.

Some may believe they sound and look good (I for one do NOT), but they are terrible for your fuel economy and performance, both mileage and acceleration suffer from this modification.

My advice would be to stick to the stock system unless the installer can guarantee (on his dime) that performance will improve.

Of course, marami naman diyan na ika-mamamtay ang pagpo-porma.

[lancer5790]

In all of my past exhaust mods, the tail-pipe was always the same size as the rest of the exhaust piping.

Is the new 3" pipe the same diameter in it's entire length? Or is it like a cone inside?

the 3" pipe which is about 6" long has the same dia all throughout but then the connection (flared like a reducer) between this 3"pipe and the muffler is 1.5" in diamtere about 1.5" long...

[ghosthunter]

the 3" pipe which is about 6" long has the same dia all throughout but then the connection (flared like a reducer) between this 3"pipe and the muffler is 1.5" in diamtere about 1.5" long...

Believe it or not, that "flared" pipe is your constriction point in your exhaust.

The change in diameter is too sudden which suddenly changes the velocity and pressure of the exhaust gasses. This adds backpressure to your car's exhaust and will just increase as engine increases RPM.

[duskylim]

Dear Sirs:

The main problem here is that spark-ignition engines throttle the charge air in order to obtain an ignitable air-fuel ratio (ranging from 12.5 to 1 up to 16.5 to 1).

As such you have a situation where there is a vacuum on the intake side and higher than atmospheric pressure on the exhaust side during all engine operation regimes up to full throttle.

As gas flows from regions of higher to regions of lower pressure, the tendency of the exhaust gases is to flow backwards towards the intake during those periods when both intake and and exhaust valves are open - this is called 'flow reversion'.

Complicating this is the pulsating flow of the whole system, for example, as the exhaust valve opens, a high-pressure (sonic) pulse travels down the exhaust manifold through the mufflers and ultimately to the atmosphere.

That pulse then expands and pushes the atmospheric air out of it's path - and the atmospheric air then rebounds and pushes back - producing an opposing pressure pulse that travels back up the system.

If that pressure pulse appears when the exhaust valve is opening - it will oppose the outflow of gases from the exhaust system and choke the flow.

That is the reason for the loss of power and economy in badly designed exhaust systems.

Timing of these sound pulses is the key to good design - the fundamental frequency being matched to the engine rpm, with harmonics being super-imposed on them.

As you can readily see, this is a task for powerful computers and very good engineers.

Best Regards,

Dusky Lim

[lancer5790]

Believe it or not, that "flared" pipe is your constriction point in your exhaust.

The change in diameter is too sudden which suddenly changes the velocity and pressure of the exhaust gasses. This adds backpressure to your car's exhaust and will just increase as engine increases RPM.

i think you're right sir. im putting back the original tail pipe asap. thanks for all your comments!

[duskylim]

Dear lancer:

As with all engineering designs, the tailpipe and exhaust systems are careful compromises.

Here the designer tries to balance the least possible backpressure - (largest possible pipes), with best possible response and fuel economy, as well as lowest possible cost.

The plain fact is, low backpressure systems (large exhaust pipe diameters) have unfavorable exhaust harmonics (performance) in the low-speed to mid-range of the engine's power band (i.e. low to mid rpm's).

As you do 95% of your driving there (at low and medium speed) and very little of the driving at full throttle (high speed) they have chosen to optimize the exhaust system for those speed ranges.

The only people who really want and need very large pipe systems on their cars are race drivers - who drive at full throttle all the time and don't really care if the car won't curb idle well with the A/C on - a racing engine's tachometer doesn't even show RPM below 1000.

So changing your tailpipe and exhaust diameters to a larger size just to make it look and sound better are often the cause of even greater problems.

Best Regards,

Dusky Lim

[theshepherd]

Sir Dusky, need an advice again.
I've changed my resonator to a bigger one but stock muffler and tailpipe.
Would there be a problem with that? My gas consumption is already fine after following the steps you've posted about the curb idle.
I'm also thinking about putting a tailpipe extension. Would that change my consumption as well?
Thanks in advance.

[lancer5790]

i replaced back my original tailpipe and my FC went down as it used to be...thanks to everyone who gave good pieces of advice..Kudos!

[duskylim]

Sir Dusky, need an advice again.
I've changed my resonator to a bigger one but stock muffler and tailpipe.
Would there be a problem with that? My gas consumption is already fine after following the steps you've posted about the curb idle.
I'm also thinking about putting a tailpipe extension. Would that change my consumption as well?
Thanks in advance.

Dear sheperd:

Its hard to say exactly, because it depends on what you mean by a bigger resonator.

Is it just physically bigger - i.e. longer and/or larger outside diameter or does it have a larger internal pipe also?

If it's just physically bigger - longer or larger outside with NO CHANGE to the INSIDE PIPE diameter then it will probably be quieter (although a larger outside diameter and greater length will make your exhaust note lower) with LITTLE or NO EFFECT on the Fuel Consumption.

If you increase the inside pipe diameter of any muffler in your system to a size larger than stock - expect to lose some low-end to mid-range torque and fuel economy.

For those who are not familiar with it a RESONATOR is a straight-through muffler with a round or oval casing around it.

The casing is filled with a sound-deadening material (typically chopped glass fiber or glass fiber mat) and the internal pipe has small holes drilled in it to allow sound waves to expand into the fill.

It is most effective in reducing the high frequency noise and makes a characteristic motorcycle exhaust sound that matches engine speed.

It is usually used as an auxiliary muffler and not as the main muffler in the exhaust system because of that motorcycle note.

When used as the main muffler it is usually very long (> 18 inches) and is called a 'Cherry Bomb' - it can wake the dead and is perfect for mga KSP.

With respect to a tailpipe extension, as long as you don't alter the existing exhaust pipe diameter and touch the stock muffler (leave that alone) you can hang anything you like off the end of your tailpipe without affecting your fuel economy and general performance.

Hope this helps.

Best Regards,

Dusky Lim

[theshepherd]

I don't need to worry then.
Thanks!

[cocoy]

are the said side effects, also affect diesel engines and turbo diesels? what would be the effects if you put a bigger diameter tail pipe after the resonator?

[duskylim]

are the said side effects, also affect diesel engines and turbo diesels? what would be the effects if you put a bigger diameter tail pipe after the resonator?

Sir - That's a good question actually.

Unlike their gasoline engine counterparts, diesel engines run UNTHROTTLED, that is, there is NO THROTTLE PLATE in the intake system.

Gasoline engines use the throttle plate to control the amount of air that the engine breathes in - which is called the 'charge'.

Adding more air than the engine can normally breathe in by itself is called 'super-charging' - and the device that does so is called a 'supercharger'.

If the device used is powered by an exhaust-driven turbine, it is called a 'turbo-supercharger' or 'turbocharger' for short.

Restricting the amount of air with a throttle plate produces a vacuum in the intake manifold of the gasoline engine.

Since diesels don't restrict the amount of air they inhale, they don't produce this engine vacuum.

This means that there is much less 'flow reversion' in a diesel.

The intake manifold in diesel engines is at or close to atmospheric pressure, while it's exhaust manifold still has exhaust pressure pulses which are higher than atmospheric pressure.

So there is still some negative pressure difference in a diesel - but much smaller than in a gas engine.

Nevertheless, this is NOT a license to install the largest (inside) diameter exhaust system on your Naturally Aspirated (No Turbo) diesel engine.

Bad exhaust harmonics can still affect your engine.

I myself have a non-turbo Mazda B2500 diesel pickup. (check out the B2200/B2500 thread).

If it were my diesel I would fit a reasonably free-flowing muffler (like Cherry Bomb's "Turbo" series) to it if the stock muffler was too restrictive - BUT I would keep the STOCK EXHAUST PIPE DIAMETER.

Note - 'Cherry Bomb' is a famous brand of American mufflers, whose many designs are familiar to the best local muffler shops - if they don't know or haven't heard of it, they're not a very experienced shop.

Note further - things are COMPLETELY different for Turbo Charged diesel engines - why?

Well the largest source of backpressure in a turbo diesel is the turbocharger itself.

So turbo diesels don't need big, restrictive mufflers to make them quiet - they already are quiet because of the turbo.

Now the amount of exhaust energy the turbo can recover from the exhaust gases depends upon the PRESSURE DIFFERENCE between the entry and exit to the turbo.

The greater the difference in entry and exit pressures, the better the turbo's performance.

That means it's best to fit the lowest possible restriction muffler AFTER the turbo - this is where you can go whole hog.

Best Regards,

Dusky Lim

[ghosthunter]

are the said side effects, also affect diesel engines and turbo diesels? what would be the effects if you put a bigger diameter tail pipe after the resonator?

With normally aspirated engines, the effects and balancing of flow vs diameter will be important.

With forced induction engines like turbocharged or supercharged, you just need to dump the exhaust gasses as quickly as possible so exhaust diameter is not as critical as the need of it to be big. In fact, with turbos, if your exhaust is too small, it will result in a slower spooling turbo.

I had a turbo on my corolla years ago and a change of the muffler (stock) to a freeflow custom muffler (my specifications) changed the characteristics of the boost from "refined" to "aggressive".

[dips15]

On a related note, the stock diameter on my car is supposedly 1.5". However, the previous owner replaced the muffler with an aftermarket one with a 2" diameter. He also removed the silencer and had the pipe go directly to the new muffler.

Since I don't like the loud sound under the car too much, I plan on adding the removed muffler/silencer. Question is, should I go back to the 1.5" diameter for this silencer or use a 2" like the muffler at the back or should I just save and change both back to the 1.5" diameter?

The guys at mufflerland is saying that the 2" diameter would improve performance. The "stock" replacement for the MB would cost more.

[ghosthunter]

On a related note, the stock diameter on my car is supposedly 1.5". However, the previous owner replaced the muffler with an aftermarket one with a 2" diameter. He also removed the silencer and had the pipe go directly to the new muffler.

Since I don't like the loud sound under the car too much, I plan on adding the removed muffler/silencer. Question is, should I go back to the 1.5" diameter for this silencer or use a 2" like the muffler at the back or should I just save and change both back to the 1.5" diameter?

The guys at mufflerland is saying that the 2" diameter would improve performance. The "stock" replacement for the MB would cost more.

I think you don't need/want to get every last horsepower from your engine.

And it takes more fuel to make more power anyway.

So it might be best for you to restore your exhaust system to it's original spec.